Photofragmentation dynamics of C₂H₅I and CF₃CH₂I at 248 nm

Abstract

Translational photofragment spectroscopy has been used to study the photodissociation dynamics of C₂H₅I and CF₃CH₂I at 248 nm. The measured anisotropies of the photofragments show that the initial absorption is the (parallel polarized) ³ Q ₀ ← N transition with a dissociation lifetime of 4 ± 2 × 10^-13s in both cases. The time of flight measurements yield the energy disposal for channels leading to I (² P _3/2) and I* (² P _1/2) for both molecules. The average energy disposed into translation is 62 per cent (I) and 72 per cent (I*) for C₂H₅I, and 36 per cent (I) and 39 per cent (I*) for CF₃CH₂I. The quantum yield for I* production is 0·67 ± 0·03 for C₂H₅I and 0·82 ± 0·07 for CF₃CH₂I. The results, combined with those of other workers, are compared to an impulsive description of the dissociation dynamics for a variety of substituted alkyl iodides. Finally a simple Landau-Zener curve crossing model is used to highlight the substantial change in curve crossing probability caused by introduction of fluorine atoms at the β position.